Shower base



FIG. 1 is a rear elevated view of the design.

FIG. 2 is a front elevated view of the design.

FIG. 3 is a front view of the design.

FIG. 4 is a rear view of the design.

FIG. 5 is a right side view of the design.

FIG. 6 is a left side view of the design; and,

FIG. 7 is a top view of the design.

The broken line is included in the drawings for the purpose ofillustrating a portion of the shower base that forms no part of theclaimed design.

CLAIM The ornamental design for a shower base, as shown and described.